This invention relates generally to signal generators of the type producing a rectangular output signal having a controllable duty cycle and frequency and, more particularly, relates to such signal generators which are digitally programmable and suited for use in association with an electronic musical instrument.
In a conventional electronic musical instrument, such as an electronic organ or the like, tone signals are typically generated in the form of rectangular waves having selected frequencies and duty cycles. Varying the frequency of such a tone signal affects the pitch of the produced sound while adjustment of the duty cycle allows for the creation of different types of orchestral sounds which are characterized by different harmonic structures. For example, experience has shown that a tone signal with a 50% duty cycle is useful for producing a clarinet-type sound whereas a tone signal having a 12.5% duty cycle is useful for producing a string-type sound. For a number of reasons, the electronic musical instrument art has in addition recently experienced a trend in the direction of digital tone signal generation. It would therefore be highly useful to provide a tone signal generator for digitally producing a rectangular wave audio tone signal whose frequency and duty cycle are both selectively controllable. Moreover, it is preferable that such a digital tone signal generator be controllable in response to suitable digital programming inputs.